Chapter 2 Identification of ecological assets, pressures and threats Rick van Dam, Renée Bartolo & Peter Bayliss Contents Executive summary 15 2.1 Introduction 16 2.2 Northern Tropical Rivers 16 2.2.1 Ecological Assets 17 2.2.2 Pressures 25 2.2.3 Threats 43 2.2.4 Assets – threats matrix 62 2.3 Daly River (Northern Territory) 64 2.3.1 Ecological assets 65 2.3.2 Pressures 77 2.3.3 Threats 84 2.3.4 Assets – threats matrix 93 2.4 Fitzroy River (Western Australia) 94 2.4.1 Ecological assets 94 2.4.2 Pressures 106 2.4.3 Threats 112 2.4.4 Assets – threats matrix 120 2.5 Flinders River (Queensland) 121 2.5.1 Ecological assets 123 2.5.2 Pressures 131 2.5.3 Threats 135 2.5.4 Assets–threats matrix 140 2.6 References 141 14 Tropical rivers risk assessments – Chapter 2 Executive summary The aquatic ecosystems of the Northern Tropical Rivers catchments are still relatively intact and, for this reason, represent an internationally significant asset. Whilst we know much about the aquatic ecosystems, particularly for specific areas (eg. Alligator Rivers Region, Ord River, Daly River), much knowledge still remains unknown and/or unquantified for most of the region. An increasing interest in agricultural and water resource development and expansion in Northern Australia has, however, drawn attention to the identification and need to ensure the maintenance of the ecological (and socio-cultural) assets and associated values of these river systems. Whilst efforts are underway to acquire new knowledge, it is also necessary to summarise existing knowledge. This chapter deals with what is currently known about the aquatic ecological assets of, and pressures and their associated threats to, the Northern Tropical Rivers study area, and in more detail, the (focus) catchments of the Daly (Northern Territory), Fitzroy (Western Australia) and Flinders Rivers (Queensland). It represents a compilation of the existing information, rather than an analysis of risk or impact; the latter aspect is dealt with in Chapters 3 and 4. This chapter focused on addressing two key questions: i. What do we currently know about the region’s aquatic ecosystems? ii. What are the pressures and threats most likely affecting the region’s aquatic ecosystems at present and into the future? Descriptions of the aquatic ecological assets focus on the: waterways; wetlands; riparian vegetation; groundwater dependent ecosystems; aquatic biodiversity; and rare, threatened and listed aquatic communities and species, at the Northern Tropical Rivers and focus catchment scales. Where appropriate key values of these assets are discussed also and, where possible, linkages are drawn between ecological and socio-cultural assets and values. Although the Northern Tropical Rivers study area is much more pristine than elsewhere in Australia and most regions of the world, many of the region’s catchments have already been substantially modified by human activities (pressures). The pressures that are considered in this chapter are: horticulture; crop production; pastoralism; urban development; tourism and recreational/customary harvest; mining; and climate change. Associated with these pressures are a range of potential threats that may impact on aquatic ecosystems and the following are considered in this chapter: groundwater extraction; surface water extraction; water impoundment; altered fire regime; land clearance/loss of native vegetation cover; introduced invasive flora; introduced invasive fauna; and contamination. Where possible, the spatial extent of the assets, pressures and threats is estimated and mapped noting, however, that such information in general is limited. To link the threats to the aquatic ecological assets (and values), asset-threat matrices are constructed with accompanying narrative that depict the potential current and emerging/future threats to the regions’ assets. Emerging/future threats are based on projected scenarios of natural resource development. The matrices are considered ‘first pass’ conceptual models that lead to the detailed assessments undertaken in Chapters 3 and 4. Whilst documenting a vast amount of literature, this chapter also identifies many gaps in information and knowledge on the biophysical attributes of the aquatic ecosystems. Paramount amongst these are: regional biodiversity, including general species distributional information, relationships between species and habitats, and the extent of endemism; surface water – groundwater interactions; distribution and functions of riparian vegetation; water quality; and the role of riverine freshwater discharge for estuarine and coastal marine productivity. However, there are many deficiencies and limitations in the spatial data for biophysical attributes and these are elaborated upon in Chapter 3. 15 Tropical rivers risk assessments – Chapter 2 2.1 Introduction This chapter represents an initial step in the problem formulation/hazard identification phase of the risk assessments in Chapters 3 and 4. It is presented separately so that readers can refer more easily to the general descriptions of the key assets and threats of the study areas. Within the scope of the assessments as defined in Chapter 1, data collation focused on the key assets, pressures and threats for the areas of interest. Thus, the aim of this phase was to identify and describe: (i) the key assets (mostly ecological, but capturing a number of overlapping values of socio-cultural and economic importance) and threats to the aquatic ecosystems at the study area and focus catchment scale; and (ii) the interactions between the ecological assets and threats (ie. an initial matrix/description of how the threats might impact on the assets and how the threats themselves might affect each other). Some of the assets data were derived from Sub-project 1 (Inventory and mapping), although the majority, as well as all the threats data, were collated as part of this project. Identification of assets and threats within the focus catchments was undertaken through a combination of reviews of existing reports and management plans, and subsequent consultations with stakeholders to check and verify the information. Both spatial and non-spatial data related to assets and threats were collated, and all spatial data have been linked to the inventory GIS developed through Sub- project 1. Ecological assets and threats information for the whole of the study area was drawn largely from regional NRM reporting processes, but also from broad scale national datasets, existing national scale reporting efforts and published research papers. Ecological assets and threats information for the focus catchments was drawn from the national scale sources and published research papers where relevant, but largely from more detailed, finer scale datasets held by the relevant government jurisdictions and other organisations (eg. local research institutions, non-government organisations – NGOs, NRM bodies). The data sources are detailed in the sections below. Where detailed synthesis information already existed in published reports (eg. NRM Plans), no attempt was made to duplicate the information in this report. Instead, summaries have been provided where possible, with the subsequent focus being on the conceptual model development and risk analysis components of the study. For more detailed information we refer the reader to the NRM reports and additional references cited throughout this report. 2.2 Northern Tropical Rivers The Northern Tropical Rivers study area comprises 51 river/drainage basins across Queensland, Northern Territory and Western Australia, from Broome in the west to Cape York in the east (see Figure 1.2). The region’s river systems are unique and comprise one of the last great river networks in relatively pristine condition in the world today, representing an internationally significant asset (Australian Tropical Rivers Group 2004). Within the region, however, there are also rivers that have been substantially modified by agricultural, urban and industrial development, such as the Ord (WA), Flinders (Qld), Leichhardt (Qld) and Darwin/Finniss River catchments (NT). In recent years (ie. the past 5–10 years), attention has been drawn to the ecological and socio-cultural assets (and associated values) of these river systems, in most part because of the increased interest in agricultural and water resource development and expansion in Northern Australia. Hamilton & Gehrke (2005) provided an excellent and concise overview of the characteristics of Australia’s tropical rivers, whilst the 16 Tropical rivers risk assessments – Chapter 2 TRIAP Sub-project 1 report by Lukacs & Finlayson (2008) provides more detail on specific biophysical attributes. Thus, the biophysical nature of the rivers is not described in detail here. 2.2.1 Ecological Assets Most efforts to characterise the status of aquatic ecosystems across this vast geographical area have been made as part of national scale activities (eg. Ball et al 2001; Norris et al 2001; Stein et al 2002; Kingsford et al 2005; Beeton et al 2006; Blanch 2006). In most cases, national scale activities cannot provide the necessary resolution or coverage to adequately describe the key ecological assets and values of the tropical rivers for regional or catchment-based risk assessments, and the concomitant management of issues that potentially threaten them. Fewer studies have concentrated solely on the Northern Tropical Rivers study area. Finlayson et al (1997) provided a short review of the management issues for wetlands across the wet-dry